Coating for diamonds

ABSTRACT

A DIAMOND HAVING A COATING WHICH COMPRISES A FIRST LAYER OF MOLYBDENUM CHEMICALLY BONDED TO THE DIAMOND, AND A SECOND LAYER ON THE FIRST LAYER SELECTED FROM THE GROUP CONSISTING OF IRON AND AN IRON-CONTAINING ALLOY, THE INTERFACE BETWEEN THE MOLYBDENUM LAYER AND THE IRONCONTAINING LAYER CONSISTING OF AN ALLOY OF IRON AND MOLYBDENUM FORMED BY MUTUAL SOLID STATE DIFFUSION AT A TEMPERATURE NOT EXCEEDING 800* C. THIS COATED DIAMOND IS PRODUCED BY DEPOSITING A LAYER OF MOLYBDENUM ON THE UNCOATED DIAMOND, DEPOSITING A LAYER OF IRON OR IRON-CONTAINING ALLOY ON THE MOLYBDENUM LAYER, AND HEATING THE COATED DIAMOND TO A TEMPERATURE OF BETWEEN 550* C. AND 800* C. IN AN INERT OR REDUCING ATMOSPHERE.

United States Patent O 3,826,630 COATING FOR DIAMONDS Alexander Rose Roy, Johannesburg, Transvaal, Republic of South Africa, assignor to De Beers Consolidated Mines Limited, Kimberley, Cape Province, Republic of South Africa No Drawing. Continuation-impart of abandoned application Ser. No. 31,389, Apr. 23, 1970. This application Sept. 14, 1972, Ser. No. 289,141

Int. Cl. B321) 15/04 US. Cl. 29-195 3 Claims ABSTRACT OF THE DISCLOSURE A diamond having a coating which comprises a first layer of molybdenum chemically bonded to the diamond, and a second layer on the first layer selected from the group consisting of iron and an iron-containing alloy, the interface between the molybdenum layer and the ironcontaining layer consisting of an alloy of iron and molybdenum formed by mutual solid state ditfusion at a temperature not exceeding 800 C. This coated diamond is produced by depositing a layer of molybdenum on the uncoated diamond, depositing a layer of iron or iron-con taining alloy on the molybdenum layer, and heating the coated diamond to a temperature of between 550 C. and 800 C. in an inert or reducing atmosphere.

CROSS REFERENCE TO RELATED APPLICATION This application is a continuation-in-part of my copending application Ser. No. 31,389, filed Apr. 23, 1970, now abandoned.

This invention relates to the metal coating of diamond.

According to the invention, there is provided a diamond having a coating which comprises a first layer of molybdenum chemically bonded to the diamond, and a secnd layer on the first layer selected from the group consisting of iron and an iron-containing alloy, the interface between the molybdenum layer and the iron-containing layer consisting of an alloy of iron and molybdenum formed by mutual solid state diffusion at a temperature not exceeding 800 C. The iron-containing alloy is preferably a nickel-iron alloy.

The coated diamond of the invention is produced by depositing a layer of molybdenum on the uncoated diamond, depositing a layer of a metal selected from iron and an iron-containing allow on the molybdenum layer, and heating the coated particle to a temperature of between 550 C. and 800 C. in an inert or reducing atmosphere. Heating the coated diamond in the specified temperature range has the effect of simultaneously causing chemical bond formation, i.e. molybdenum carbide forma tion, at the diamond/molybdenum interface and the formation at the iron-containing layer/molybdenum interface on an alloy of molybdenum and iron formed by mutual solid state diflusion. This provides the coated diamond with extremely strong interfacial bond strengths. Furthermore the iron-containing layer readily bonds with the matrices of abrasive tools such as saws or wheels. Thus it has been observed that the tendency for dislodgment of the diamond particles from the abrasive surfaces of such tools during abrasive operations is reduced, as is evidenced by G-ratio results obtained.

The layer of molybdenum may be deposited on the diamond by any suitable means well known in the art, for example, by vacuum deposition (Vacuum Deposition of Thin Films by L. Holland, Chapman and Hall, 1st Edition 1956) or by chemical means.

Once the intermediate layer has been deposited on the diamond, the outer iron-containing layer may be electroplated thereto in a manner also well-known in the art.

If desired, a flashing of copper may be provided on the outer surface of the iron-containing layer.

The molybdenum deposition is preferably achieved by a well-known chemical method. Firstly, molybdic acid is dissolved in sulphuric acid and then extracted with acetylacetone to form a complex which is soluble in acetylacetone and chloroform. Heating this complex with the diamond and subsequent reduction with hydrogen causes the necessary decomposition of the molybdenum complex. The layer of iron or iron-containing alloy is then electroplated on to the molybdenum-coated diamond. Heating to 550 C.-800 C. in an inert or reducing atmosphere results in the desired molybdenum-diamond chemical bond and the simultaneous mutual solid state diffusion of iron from the iron-containing layer in the molybdenum.

The following examples illustrate the preparation of coated diamonds according to the invention.

Example 1 to US. mesh RD diamonds (resin bond diamonds) were used. The diamonds were first coated with a 3% (by weight of the diamond) covering of molybdenum by the method described above.

A layer of iron was then deposited on the molybdenum coated diamond using a well known electrolytic coating method. The coated diamond was heated to 600 C. in an inert or reducing atmosphere to achieve the formation of molybdenum carbide at the diamond/ molybdenum interface and mutual solid state diffusion of iron in the molybdenum. A copper flashing was then electrolytically deposited on the outer surface of the coated diamond. The composite product has an iron layer of 97% and a copper flashing of 3%, both percentages being by weight of the diamond.

Example 2 A 3% molybdenum covering was deposited on RD diamonds as in Example 1. On this coated diamond, there was deposited a layer of nickel-iron alloy, containing 43% nickel, by a standard method of electroplating as described in Electrodeposition of Alloys Principles and Practice, Volume II, Abner Brenner, Academic Press, New York and London, 1963, pages 265-314. The composite diamond is then heated in an inert or reducing atmosphere to a temperature of 550-800 C. to achieve the formation of molybdenum carbide and the mutual solid state diffusion of the iron in molybdenum. The alloy outer layer comprised 97% by weight of the diamond. A 3% copper flashing was then electrolytically deposited on the alloy layer.

Comparative ResultsDry Grinding Conditions Product: G-ratio Clad Diamonds of prior art 16.6 Coated Diamonds of this Example 19.2

In the above tests, standard grinding conditions were employed using a resin bond wheel. (Carbide Workpiece):

Dry Grinding Conditions:

Machine Tacchella 6 ALP. Wheel Speed 3200 r.p.m. Wheel Size 5" x face D 1 1V9. Table traverse speed 2 m./min. Infeed .050 mm. Total infeed 1.0 mm. Specimen face size /2 X A".

The G-ratio is the ratio of the amount of metal removed from the workpiece to the amount of grinding tool used during the grinding operation. Obviously, the higher the G-ratio the better the grinding properties of the particular grinding wheel. The grinding wheels con taining coated diamonds of the invention, as will be clearly seen from the above results, have superior grinding properties over wheels containing coated diamonds of the prior art.

The coated diamonds of the invention are particularly suitable for use in resin bond abrasive tools, but may also be useful in metal bond and saw abrasive tools as well.

What is claimed is:

1. A diamond having a coating which comprises a first layer of molybdenum chemically bonded to the diamond, and a second layer on the first layer of a material se lected from the group consisting of iron and an iron-containing alloy, the interface between the molybdenum layer and the iron-containing layer consisting of an alloy of iron and molybdenum formed by mutual solid state dif fusion at a temperature not exceeding 800 C.

2. A diamond according to claim 1 wherein the ironcontaining alloy is a nickel-iron alloy.

4 3. A diamond according to claim 1 comprising a copper flashing covering the outer surface of the iron-containing layer.

References Cited UNITED STATES PATENTS 2,020,117 11/1935 Johnston 204-6 2,382,666 8/1945 Rohrig et al. 51309 2,876,139 3/1959 Flowers 117-131 3,306,720 2/1967 Darrow 51-309 3,351,543 11/1967 Vanderslice 51309 X 3,356,473 12/ 1967 Hull et al. 51-309 L. DEWAYNE RUTLEDGE, Primary Examiner E. L. WEISE, Assistant Examiner US. Cl. X.R. 

